This invention concerns a molding method, in which a synthetic resin or rubber is molded upon an insert (work piece) which is set beforehand inside a mold (this method is referred to hereinafter as the xe2x80x9cinsert molding or insert molding methodxe2x80x9d), and a mold to be used in said insert molding method, and discloses an insert molding method and mold that are excellent in terms of prevention of insert breakage, prevention of burr formation, and manufacture, operation, maintenance, etc. of molds.
This invention provides in an insert molding method, wherein an upper mold and a lower mold are disposed so as to oppose each other and a cavity at the upper mold side is filled with molten resin or rubber material that is injected through a gate to perform injection molding of the resin or rubber around an insert set at the lower mold side, an insert molding method and mold characterized in that a movable supporting member, which sets the above mentioned insert, is fitted in a recessed part formed on the upper face of the above mentioned lower mold, the position of the center of gravity at the lower face of the movable supporting member is supported and pressed towards the upper mold side by the tip of a shaft of a pressing mechanism, and a gap is made to exist between the side face part of the above mentioned recessed part and the side face part of the movable supporting member to cause the movable supporting member to tilt about the point at which the movable supporting member is pressed and supported by the above mentioned shaft inside the above mentioned recessed part so that the upper face of the insert will be in uniform surface contact with the lower face of the upper mold.
1. Field of the Invention
This invention concerns a molding method, in which molding of a synthetic resin or rubber is performed upon an insert (work piece) which is set beforehand inside a mold(this method is referred to hereinafter as the xe2x80x9cinsert molding or insert molding methodxe2x80x9d), and a mold to be used in said insert molding method.
2. Description of the Prior Art
In an insert molding method, molding by synthetic resin is performed upon a formed part, called an insert or a work piece, which is set beforehand inside a molding mold to form resin molded parts on the upper surface or surroundings of the insert, and is widely used in the manufacture of various electronic parts, etc. Though insert molding method is applied to various resin molding methods, this invention is limited to the injection molding method.
The insert to be set beforehand inside the mold may be a worked resin molded part (of plate shape, rod shape, box shape, or other shape) or may be a part made from a non-resin material, such as metal, glass, ceramic, carbon, etc.
In many cases, the insert is not manufactured with high dimensional precision, and for example, in the case where inserts that are scattered in the thickness dimension are set in molds to perform injection molding, depending on the insert, a gap may form at the surface of contact of a part of the insert and an upper mold even if clamping is performed and the resin that is injected into this part may flow out and become a burr.
The details of the above shall now be described with reference to drawings. As shown in FIG. 3, when an insert 1, having the shape of a flat plate, is low in working precision and has a thickness difference such that h1 less than h2 and mold clamping is performed upon setting this insert on the upper face of a lower mold 2, the upper surface portion of insert 1 at the side of greater thickness (the h2 side) will contact the lower face of an upper mold 3 while a gap will form at the side of smaller thickness (the h1 side). Put in another way, since insert 1 is inclined, a gap will form at the peripheral lower face of a cavity (recessed part) 4 prepared at the upper mold 3 side. Since cavity 4 is a part that will become a molded product made of synthetic resin, if injection of plastic via a gate 5 is performed in the condition where there is a gap at the lower face, a burr 7 will form at the lower end part of the resin molded product 6 as shown in FIG. 4.
In particular, with the injection molding method, since the resin is injected at high pressure, resin can leak out from even an extremely small gap and give rise to burrs. If a low injection pressure is set to prevent the formation of burrs, the precision and physical properties of the molded product will become poor.
Several modifications for preventing the above-described formation of burrs in insert molding have been tried and the results of such modifications have been disclosed for example in Japanese Unexamined Patent Publication No. Hei-8-288326.
Resolution of the problem of burr formation in insert molding is demanded since it leads not only to manufacturing loss but also to increased manufacturing cost resulting from the necessity for burr removal work.
The above mentioned Japanese Unexamined Patent Publication No. Hei-8-288326 teaches that by using a resilient member (a plurality of coiled springs) to support the lower face side of a supporting member on which an insert is set, the scattering of the thickness of inserts can be absorbed to prevent the formation of burrs. However, since the dimensional scattering of inserts is not fixed and there are various forms of scattering, supporting by a plurality of springs that apply a uniform force on the insert supporting member does not provide a satisfactory solution.
Also as has been mentioned above, inserts are not limited to pressed metal inserts and synthetic resin inserts but also include ceramic, carbon, and glass inserts that can break readily at low impact force, and especially with the latter types of inserts, breakage of the insert set in the mold in the clamping process can occur and lead to manufacturing loss when there is scattering of the precision of outer shape.
This invention has been made in view of the above and an object thereof is to present an insert molding method and mold that are excellent in terms of prevention of insert breakage, prevention of burr formation, and manufacture, operation, maintenance, etc. of molds.
The insert molding method and the mold to be used in inserting molding by this invention are characterized in having the following arrangements.
A. In an insert molding method, wherein an upper mold and a lower mold are disposed so as to oppose each other and the cavity at the upper mold side is filled by molten resin or rubber material that is injected via a gate to perform injection molding of the resin or rubber around an insert set at the lower mold side, an insert molding method characterized in that a movable supporting member, which sets the above mentioned insert, is fitted in a recessed part formed on the upper face of the above mentioned lower mold, the position of the center of gravity at the lower face of the movable supporting member is supported and pressed towards the upper mold side by the tip of a shaft of a pressing mechanism, and a gap is made to exist between the side face part of the above mentioned recessed part and the side face part of the movable supporting member to cause the movable supporting member to tilt about the point at which the movable supporting member is pressed and supported by the above mentioned shaft inside the above mentioned recessed part so that the upper face of the insert will be in uniform surface contact with the lower face of the upper mold.
B. In an insert molding mold, which is comprised of (a) an upper mold, (b) a lower mold, which is disposed so as to oppose the upper mold, (c) a recessed part, formed on the upper face of the above mentioned lower mold, (d) a movable supporting member, which is fitted into the recessed part, (e) an insert setting part, which is provided on the upper face of the movable supporting member, (f) a cavity, provided on the mold surface at the lower face of the above mentioned upper mold that opposes the above mentioned insert, and (g) a gate, provided at the upper mold for injection of molten resin or rubber material into the cavity, and is arranged for performing injection molding of resin or rubber material around the insert set on the upper face of the above mentioned movable supporting member by filling of the above mentioned cavity of the upper mold by injection of the molten resin or rubber material via the gate, an insert molding mold characterized in having (h) a pressing mechanism, which has a shaft that supports and presses the position of the center of gravity of the lower face of the above mentioned supporting member towards the upper mold side and in that (i) a gap is formed between the side face part of the above mentioned recessed part and the side face part of the movable supporting member and the above mentioned movable supporting member is enabled to tilt about the point of pressing and support by the above mentioned shaft inside the above mentioned recessed part so that the upper face of the insert will be in surface contact with the lower face of the upper mold.
C. An insert molding method as set forth in A above, wherein the outer shape (planar shape) of the side face of the above mentioned movable supporting member is formed to be similar to the outer shape (planar shape) of the side face of the insert.
D. An insert molding mold as set forth in B above, wherein the outer shape (planar shape) of the side face of the above mentioned movable supporting member is formed to be similar to the outer shape (planar shape) of the side face of the insert.
E. An insert molding method as set forth in A or C above, wherein the gap between the side face part of the above mentioned recessed part and the side face part of the movable supporting member is large at the side close to the upper mold and small at the side away from the upper mold.
F. An insert molding mold as set forth in B or D above, wherein the gap between the side face part of the above mentioned recessed part and the side face part of the movable supporting member is large at the side close to the upper mold and small at the side away from the upper mold.
G. An insert molding method as set forth in A or C above, wherein the gap between the side face part of the above mentioned recessed part and the side face part of the movable supporting member is arranged to be greatest at the position closest to the upper mold and to decrease gradually and become zero with the distance from the upper mold.
H. An insert molding mold as set forth in B or D above, wherein the gap between the side face part of the above mentioned recessed part and the side face part of the movable supporting member is arranged to be greatest at the position closest to the upper mold and to decrease gradually and become zero with the distance from the upper mold.
An embodiment of this invention shall now be described based on the attached drawings. This embodiment is an example of the case where the upper mold is a fixed mold and the lower mold is a movable mold.